The present invention relates to epoxy resin compositions suitable for printed circuit boards and printed circuit boards using the same.
With an increasing demand for more compactness and high performance of electronics devices, a higher density packaging of printed circuit boards to be included therein is progressing by provisions of multilayered and thin film lamination, a reduced diameter of plated throughholes, a narrow gap between holes and the like. Further, for printed circuit boards to be mounted in information terminal equipment such as a cellular phone, a mobile computer and so on, which requires plastic packaging directly to mount a MPU on its printed circuit board, or on other types of printed circuit boards suitable for various types of modules, it is demanded to be able to process a large quantity of information at a higher speed, thereby requiring a faster signal processing speed, a lower transmission loss, and further down-sizing in the components and system. Therefore, a finer pattern wiring is demanded more than ever with the trend for the higher density electronic packaging.
A substantially improved material having an excellent heat endurance and a high Tg is demanded for such printed circuit boards and those for a module which mount MPUs thereon in order for the reliability of their circuit connections to be ensured fully. However, because conventional resin materials having a high Tg tend to be mechanically hard and brittle, there is such a disadvantage that they have a low adhesiveness with a copper foil. Any resin material having a low adhesion with the copper foil tends to cause a peel-off and /or disconnection of wiring during molding and packaging of a substrate. Therefore, the adhesion property with the copper foil will become more vital with an advancing finer pattern wiring technique.
Conventional printed circuit boards using an epoxy resin group which is cured with dicyandiamide have been widely used. However, this epoxy resin group cured with dicyandiamide has a disadvantage that its hygroscopic property tends to increase. Therefore, it is becoming difficult to satisfy an increasing insulation reliability required for realizing a next-generation printed circuit board having a higher packaging density.
In contrast, a group which uses a multifunctional phenol resin as its curing agent has a low water absorption, and can provide for a printed circuit board having a Tg higher than 170xc2x0 C. However, as mentioned previously, the resin material having a high Tg is hard and brittle, and still more, the multifunctional phenol cured group has a lower adhesive strength with a copper foil because of its lower polarity of the resin compared with the dicyandiamide cured group.
A method for improving the adhesive property between the copper foil and the resin which has been practiced heretofore includes a copper foil treatment using a coupling agent and the like as disclosed in JPA Laid-Open No. 54-48879. However, for such hard and brittle resin groups having a higher Tg, there cannot be attained any sufficient chemical bonding therebetween merely by the treatment using commercially available coupling agents, such chemical bonding being inferior to that of conventional FR-4. Another method for treating the copper foil with a silane coupling agent has a problem that residue remaining on the substrate after circuitry formation cause contamination in the subsequent plating process and adversary affect the adhesion with solder resists.
The present invention has been contemplated to solve these problems associated with the prior art and provide for an epoxy resin composition and a printed circuit board using the same, which features a low hygroscopic property, an excellent heat endurance and a good adhesion with copper foils.
Namely, the epoxy resin composition and the printed circuit board using the same are made of an epoxy resin composition which comprises essentially (a) an epoxy resin, (b) a multi-functional phenol group, (c) a hardening accelerator, and (d) a compound with a triazine or isocyanuric ring, or a compound which contains nitrogen 60 weight percent or less without containing a urea derivative.
Further, in the epoxy resin composition for use in the printed circuit board according to the invention, preferably, its phenol hydroxyl group in the multi-functional phenol of (b) is in a range of 0.5 to 1.5 equivalent weight relative to the epoxy group of the epoxy resin; the hardening accelerator of (c) is in a range of 0.01 to 5 weight part relative to a hundred weight part of the epoxy resin; and the compound of (d) with a triazine or isocyanuric ring, or the compound which contains nitrogen of 60 weight percent or less without containing urea derivative is contains nitrogen in a range of 0.1 to 10 weight percent relative to a solid resin part. Further, more preferably, in addition to the above (a) to (d), the epoxy resin composition of the invention contains (e) a flame-retardant agent, which is preferably a tetrabromobisphenol A or a glycidyl ether of tetrabromobisphenol A.
Still further, the epoxy resin composition for use in the printed circuit board according to the invention described above is provided as a varnish, which is impregnated into a base material, dried to provide for a prepreg, on one or both surfaces of the prepreg, a plurality of which may be laminated, a metal foil is deposited, then they are heated under pressure to form the printed circuit board.
The preferred embodiments of the invention will be described in detail in the following.
The epoxy resin of (a) described above is selected from the group which includes: a bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenol type epoxy resin, phenol novolac type epoxy resin, crezol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin; phenol salicylate aldehyde novolac type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, glycidyl ether type epoxy resin, and other compounds such as a bi-functional phenol group glycidyl ether compound, bi-functional alcohol glycidyl ether compound, polyphenol group glycidyl ether compound, polyphenol glycidyl ether compound and its hydride or halogenate. However, it is not limited to the above, and may be used in combination of these compounds.
The multifunctional phenol group of (b) described above is selected from the group which includes: a bisphenol F, bisphenol A, bisphenol S, polyvinyl phenol, and a novolac resin or its halogenate which is obtained by addition condensation of a phenol group such as phenol, crezol, alkylphenol, catechol, bisphenol F, bisphenol A and bisphenol S with an aldehyde group. A molecular weight of any of these compounds is not limited particularly, and it may be used in combination. A quantity of addition of its phenol hydroxyl group is preferably in a range of 0.5 to 1.5 equivalent weight relative to the epoxy group of the epoxy resin. If outside this range, a problem arises that its dielectric property and heat endurance may be deteriorated.
The hardening accelerator described above (c) may be any compound if it has a function to accelerate ether chemical reaction of the epoxy group with phenol hydrate group, which includes, for example, an alkaline metal compound, alkaline earth metal compound, imidazole compound, organic phosphorus compound, secondary amine, tertiary amine, tetra ammonium salt and the like. When an imidazole compound is used wherein its imino group is masked with acrylonitrile, isocyanate, melamine acrylate or the like, advantageously, a prepreg that has an excellent pot life stability twice or more better than that of the conventional prepreg can be provided.
The imidazole compound used here includes: imidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecyl imidazole, 4,5-diphenylimidazole, 2-methylimidazoline, 2- 2-phenylimidazoline, 2-undecylimidazoline, 2-heptadecylimidazoline, 2-isopropylimidazole, 2,4-dimethyl imidazole, 2-phenyl-4-methylimidazole, 2-ethylimidazoline, 2-isopropylimidazoline, 2,4-dimethylimidazoline, 2-phenyl-4-methylimidazoline and the like. The masking agent includes acrylonitrile, phenylen diisocyanate, toluene diisocyanate, napthalen diisocyanate, methyl bisphenyl isocyanate, isophorone diisocyanate, melamine isocyanate and the like. This hardening accelerator may be used in combination. A quantity thereof is preferably in a range of 0.01 to 5 weight part with respect to a hundred weight part of the epoxy resin. At 0.01 weight part orless thereof, its acceleration effect becomes negligible, and at more than 5 weight part thereof, the pot life stability deteriorates. deteriorates.
The compound of (d) having triazine ring or isocyanuric ring, or the compound containing nitrogen less than 60 weight percent without containing urea derivative includes, for example, an aromatic amine type epoxy resin, aliphatic amine type epoxy resin, hydantoin type epoxy resin, glycidyl amine type epoxy resin, isocyanurate type epoxy resin, cyanurate group, isocyanurate group, melamine group, an addition condensate of phenol group, a compound having a triazine ring, and aldehyde group, and glycidyl ether thereof, however, it is not limited thereto. These compounds may be of any type or may be used in combination. Preferably, a nitrogen content contained in these compounds is in a range of 0.1 to 10 weight percent compared to a whole solid resin part of the epoxy resin composition used in the printed circuit board. At less than 0.1 weight percent of the nitrogen content, it is difficult to improve the adhesive strength with the copper foil, and at excess of 10 weight percent thereof, the water absorption rate increases.
The flame retardant agent of (e) described above may be of any type of flame retardant agents commercially available, which includes, for example, a haloganate compound of any of the following: a bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, crezol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, phenol salicylic aldehyde novolac type epoxy resin, cyclic aliphatic epoxy resin, aliphatic chain epoxy resin, glycidyl esther type epoxy resin, and other haloganate compounds of bisphenol A, bisphenol F, bisphenol S, polyvinyl phenol, or those of the phenol group including phenol, crezole, alkylphenol, catechol, bisphenol with a novolac resin of aldehyde group. However, it is not limited thereto, and an antimonious trioxide, tetraphenyl phosphine or the like may be used in combination-as well.
When applying or impregnating the epoxy resin composition for use in the printed circuit board into the base material, a solvent may be used. Such solvents include acetone, methylethyl ketone, toluene, xylene, methyl isobuthyl ketone, ethyl acetate, ethylene glycol monomethylether, N, N-dimethyl acetoamide, methanol, ethanol and the like, and these may be used in combination.
The varnish using the epoxy resin composition for use in the printed circuit board obtained by blending the above- mentioned materials from (a) to (e) is impregnated into a base material such as a glass fiber, unwoven glass cloth or paper, or into any cloth without using glass, then dried in an oven at temperatures in a range from 80 to 200xc2x0 C., thereby obtaining a prepreg of the epoxy resin composition for use in the printed circuit board. The prepreg is heated under pressure at temperatures from 150 to 250xc2x0 C. and at 20 to 80 Kgf/cm2 for 0.3 to 3 hours, which is then used to manufacture a printed circuit board or a metal-clad laminate.
The process of heating of the prepreg is provided for removing the solvent when it is used, and for eliminating the fluidity at room temperatures when the solvent is not used.
The epoxy resin composition and the printed circuit board using the same are provided according to the invention, which feature a low water absorption, a high heat endurance and an improved adhesion with copper foils, wherein the epoxy resin composition is comprised of (a) an epoxy resin, (b) a multifunctional phenol group, (c) a hardening accelerator, and (d) a compound having a triazine ring or isocyanuric ring, or a compound containing nitrogen at 60 weight percent or less without containing urea derivatives.